Diabetes Mellitus (cont.)
Why is blood sugar checked at home?
Home blood sugar (glucose) testing is an important part of controlling blood
sugar. One important goal of diabetes treatment is to keep the blood glucose
levels near the normal range of 70 to 120 mg/dl before meals and under 140 mg/dl
at two hours after eating. Blood glucose levels are usually tested before and
after meals, and at bedtime. The blood sugar level is typically determined by
pricking a fingertip with a lancing device and applying the blood to a glucose
meter, which reads the value. There are many meters on the market, for example,
Accu-Check Advantage, One Touch Ultra, Sure Step and Freestyle. Each meter has
its own advantages and disadvantages (some use less blood, some have a larger
digital readout, some take a shorter time to give you results, etc). The test
results are then used to help patients make adjustments in medications, diets,
and physical activities.
There are some interesting developments in blood glucose monitoring.
Currently, at least three continuous glucose sensors are approved in the United States (Dexcom, Medtronic and Navigator). The new
continuous glucose sensor systems involve an implantable cannula placed just
under the skin in the abdomen or in the arm. This cannula allows for frequent
sampling of blood glucose levels. Attached to this is a transmitter that sends
the data to a pager-like device. This device has a visual screen that allows the
wearer to see, not only the current glucose reading, but also the graphic
trends. In some devices, the rate of change of blood sugar is also shown. There
are alarms for low and high sugar levels. Certain models will alarm if the rate of
change indicates the wearer is at risk for dropping or rising blood glucose too
rapidly. The Medtronic version is specifically designed to interface with their
insulin pumps. However, at this time the patient still must manually approve any
insulin dose (the pump cannot blindly respond to the glucose information it
receives, it can only give a calculated suggestion as to whether the wearer
should give insulin, and if so, how much). All of these devices need to be
correlated to fingersticks for a few hours before they can function
independently. The devices can then provide readings for 3-5 days.
Diabetes experts feel that these blood glucose monitoring devices give
patients a significant amount of independence to manage their disease process;
and they are a great tool for education as well. It is also important to
remember that these devices can be used intermittently with fingersticks. For
example, a well-controlled patient with diabetes can rely on
fingerstick glucose
checks a few times a day and do well. If they become ill, if they decide to
embark on a new exercise regimen, if they change their diet and so on,
they can use the sensor to supplement their fingerstick regimen, providing more
information on how they are responding to new lifestyle changes or stressors.
This kind of system takes us one step closer to closing the loop, and to the
development of an artifical pancreas that senses insulin requirements based on
glucose levels and the body's needs and releases insulin accordingly - the
ultimate goal.
Hemoglobin A1c (A1c)
To explain what an hemoglobin A1c is, think in simple terms. Sugar sticks, and when it's
around for a long time, it's harder to get it off. In the body, sugar sticks
too, particularly to proteins. The red blood cells that circulate in the body
live for about three months before they die off. When sugar sticks to these cells,
it gives us an idea of how much sugar is around for the preceding three months. In
most labs, the normal range is 4%-5.9 %. In poorly controlled diabetes, its 8.0%
or above, and in well controlled patients it's less than 7.0% (optimal is
<6.5%). The benefits of measuring A1c is that is gives a more reasonable and
stable view of what's happening over the course of time (three months), and the
value does not bounce as much as finger stick blood sugar measurements. There is
a direct correlation between A1c levels and average blood sugar levels as
follows.
While there are no guidelines to use A1c as a screening tool, it gives a
physician a good idea that someone is diabetic if the value is elevated. Right
now, it is used as a standard tool to determine blood sugar control in patients
known to have diabetes.
| A1c(%) |
Mean blood sugar (mg/dl) |
| 6 |
135 |
| 7 |
170 |
| 8 |
205 |
| 9 |
240 |
| 10 |
275 |
| 11 |
310 |
| 12 |
345 |
The American Diabetes Association currently recommends an A1c
goal of less than 7.0%. Other Groups such as the American Association of Clinical
Endocrinologists feel
that an A1c of <6.5% should be the goal.
Of interest, studies have shown that there is about a 10% decrease in
relative risk for microvascular disease for every 1% reduction in A1c. So, if a
patient starts off with an A1c of 10.7 and drops to 8.2, though there are not
yet at goal, they have managed to decrease their risk of microvascular
complications by about 20%. The closer to normal the A1c, the lower the absolute
risk for microvascular complications. Data also suggests that the risk of
macrovascular disease decreases by about 24% for every 1% reduction in A1c
values.
It should be mentioned here that there are a number of
conditions in which an A1c value may not be accurate. For example, with
significant anemia, the red
blood cell count is low, and thus the A1c is altered. This may also be the case
in sickle cell disease and
other hemoglobinopathies.
Next: What are the acute complications of diabetes? »
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